1. Field of the Invention
The present invention relates to bone clamps, and, more particularly, to a bone clamp having an improved rachet mechanism.
2. Description of the Related Art
Bone clamps are well known in the medical profession and can be used, e.g., to engage broken bones for movement thereof. Bone clamps are reusable devices and therefore longevity is a desirable characteristic. Generally, bone clamps are utilized to move broken bones into aligned position or hold bone fragments together while surgical procedures (e.g., installation of a screw, plate, pin, or wire) are performed. When performing surgery to repair a broken bone, it is important to clamp the bone fragments together while a mending device (e.g., a screw, plate, pin, or wire) is being installed so that the bone fragments can be maintained in alignment with substantially no gaps therebetween. For example, bone clamps may be utilized to hold bone plates in position across a bone fracture and/or to align the fractured bones while the bone plate(s) are affixed thereto.
Typically, bone clamps utilize a rachet mechanism to control movement of the bone clamp and to maintain the bone clamp in locked position once it is operatively positioned. Ratchets utilized with prior art bone clamps are generally of two types: (1) a unidirectional rachet, e.g., of the type utilized with standard forceps, and (2) a bidirectional ratchet having a selectively actuatable lock mechanism to retain the pawl in locked position between two consecutive rachet teeth.
Ratchets of the second type (i.e., bidirectional ratchets) utilize rachet teeth formed by opposing ramp surfaces 90, 92 as illustrated in FIG. 10. Similarly, pawl 94 is formed by opposing ramp surfaces 96, 98. Opposing ramp surfaces 90, 92 and 96, 98 are substantially linear and culminate in a point. As pawl 94 is moved relative to the ratchet teeth, the peak of the pawl contacts the peaks of successive ratchet teeth and the interaction forces between the ratchet and the pawl will be concentrated at the peak of the pawl and the peaks of the ratchet teeth. The concentration of force causes a substantial shear stress at the peaks which will lead to fractures and rounding of the peaks (both of the pawl and of the ratchet teeth) as the bone clamp is repeatedly used. Such rounding of the peaks impairs the utility of the rachet since the pawl will be easily moveable relative to the rachet teeth and there will exist less contact surface area between the pawl and subsequent rachet teeth when the pawl is locked in position therebetween.
Ratchets of the first type (i.e., unidirectional ratchets) are less desirable than bidirectional ratchets since they assist in controlling movement of the clamp actuating members in one direction only. Furthermore, unidirectional ratchets utilize pawls and ratchet teeth having substantially linear ramp surfaces culminating in a point and therefore suffer from the same drawbacks as described above with respect to bidirectional ratchets.
What is needed in the art is a bone clamp having a bidirectional rachet for controlling the movement of the clamp actuating members which does not suffer from the disadvantages described above.
The present invention comprises a bone clamp having a bidirectional rachet mechanism which does not utilize substantially linear opposing ramp surfaces culminating in a point to form the pawl and the ratchet teeth. The rachet mechanism of the current invention comprises a plurality of rachet teeth formed from a plurality of rounded peaks having a plurality of curved valleys therebetween, and a curved pawl having substantially the same curvature as the valleys of the rachet teeth. The rounded structure of the rachet and pawl of the present invention eliminates the interaction of a pair of sharp peaks as in the prior art. The interaction forces between the rachet and the pawl of the current invention are more evenly distributed than in the ratchet mechanisms of the prior art due to the rounded surfaces of the ratchet teeth and the pawl of the present invention. Therefore, the present invention lessens the detrimental effect of the interaction forces between the ratchet and the pawl.
The invention, in one form thereof, comprises a bone clamp including a first clamp member and a second clamp member as well as a ratchet mechanism, which is resistive to shear stress, for controlling actuation of the first clamp member. Actuation of first clamp member relative to the second clamp member places the bone clamp in either a clamped or an unclamped position.
The invention, in another form thereof, comprises a bone clamp including a first clamp member and a second clamp member as well as a ratchet mechanism for controlling actuation of the first clamp member relative to the second clamp member. The ratchet mechanism of this form of the current invention includes a plurality of ratchet teeth comprising a plurality of curved peaks with a plurality of valleys therebetween, and a pawl which selectively contacts each of the plurality of ratchet teeth.
The invention, in yet another form thereof, comprises a bone clamp including a first clamp member and a second clamp member as well as a ratchet mechanism for controlling actuation of the first clamp member relative to the second clamp member. The ratchet mechanism of this form of the current invention includes a plurality of ratchet teeth comprising a plurality of peaks with a plurality of valleys therebetween and a curved pawl selectively contacting each of the plurality of ratchet teeth.
The invention, in another form thereof, comprises a bone clamp including a first clamp member and a second clamp member as well as a rachet mechanism for controlling actuation of the first clamp member relative to the second clamp member. Actuation of the first clamp member relative to the second clamp member places the bone clamp in either a clamped or an unclamped position. The rachet mechanism of this form of the current invention includes a plurality of rachet teeth comprising a plurality of peaks with a plurality of curved valleys therebetween, and a pawl which selectively contacts each of the plurality of rachet teeth.
An advantage of the present invention is the ability to provide a bidirectional rachet in which interaction forces between the pawl and rachet teeth are more evenly distributed than in the bidirectional ratchets of the prior art.